Double-reflux pressure swing adsorption separation method for methane-nitrogen-oxygen mixed gas by two-stage method
The two-stage double-reflux pressure swing adsorption separation method using a methane-nitrogen-oxygen mixture utilizes carbon molecular sieve separation materials to achieve efficient methane separation in low-concentration methane coalbed methane. This solves the problem of low methane utilization in low-concentration methane coalbed methane and achieves high-purity and high-recovery methane separation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2026-04-20
- Publication Date
- 2026-05-26
AI Technical Summary
Existing technologies struggle to efficiently separate low-concentration methane-nitrogen-oxygen mixtures, resulting in low methane utilization rates in low-concentration methane coalbed methane.
A two-stage double-reflux pressure swing adsorption separation method using a methane-nitrogen-oxygen mixture is employed. Through the alternating operation of first-stage and second-stage high- and low-pressure towers, adsorption and displacement are carried out using carbon molecular sieve separation materials to achieve efficient separation of methane.
High-purity and high-recovery methane separation was achieved at room temperature and low adsorption pressure, reducing energy consumption and costs. It is suitable for the treatment of low-concentration methane coalbed methane and improves the utilization value of methane.
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Figure CN122076173A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of gas separation technology, and in particular to a two-stage double-reflux pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture. Background Technology
[0002] Methane is not only a low-carbon, clean fossil fuel resource, but also the second largest anthropogenic greenhouse gas after carbon dioxide. In 2023, global methane emissions from the energy sector approached 130 million tons, accounting for more than one-third of total anthropogenic emissions, mainly from emissions during coal mining and uncontrolled leaks in oil and gas operations. Coalbed methane emissions are a significant component, accounting for approximately 40% of global anthropogenic emissions. Therefore, promoting the effective utilization of coalbed methane has significant synergistic benefits, not only improving mine safety but also supplementing clean energy and reducing greenhouse gas emissions.
[0003] The key to achieving efficient utilization of coalbed methane lies in the separation process after pretreatment. After desulfurization and other pretreatment, the main components of coalbed methane are nitrogen, oxygen, and methane. Therefore, the separation process primarily involves separating methane from nitrogen and oxygen. Currently, the main technologies for separating methane, nitrogen, and oxygen include cryogenic separation, pressure swing adsorption (PSA), and membrane separation. Cryogenic separation technology requires significant investment and has high operating costs, making it suitable for large-scale processing. Membrane separation technology offers high separation efficiency but is highly dependent on membrane materials, technically challenging, and suffers from short lifespan and susceptibility to damage; it is currently still under development and has not yet achieved industrial application. In contrast, PSA technology features simple equipment, can operate flexibly within a range from ambient temperature and pressure to high temperature and pressure, and offers advantages such as high operational flexibility, high automation, and low cost and energy consumption, demonstrating significant application potential in the field of methane-nitrogen-oxygen separation.
[0004] Based on this, a tiered utilization model has been initially established for methane utilization in coalbed methane: coalbed methane with a methane volume concentration higher than 30% is mainly used for domestic and industrial gas production, compressed natural gas production, and power generation; coalbed methane with a methane volume concentration between 8% and 30% is mainly used for internal combustion engine power generation; and for low-concentration coalbed methane with a methane volume concentration below 8%, its use in flameless oxidation and other applications is being promoted. However, traditional pressure swing adsorption (PSA) processes for methane are mostly designed for coalbed methane with a methane concentration higher than 30%, and research on processes for low-concentration methane coalbed methane is still relatively limited, failing to further realize the value of low-concentration methane coalbed methane. Moreover, since methane and nitrogen molecules have similar particle sizes, existing separation processes are insufficient for separating low-concentration methane coalbed methane.
[0005] Therefore, it is of great significance to develop a pressure swing adsorption separation method for methane-nitrogen-oxygen mixtures with low methane concentration, thereby improving the utilization rate of methane in low-concentration methane coalbed methane. Summary of the Invention
[0006] In view of this, the present invention provides a two-stage double-reflux pressure swing adsorption separation method for methane-nitrogen-oxygen mixtures to solve the problems of difficulty in separating methane-nitrogen-oxygen mixtures with low methane concentration and low utilization rate of methane in low-concentration methane coalbed methane.
[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a two-stage method for the separation of a methane-nitrogen-oxygen mixture using dual reflux pressure swing adsorption, comprising the following steps: A methane-nitrogen-oxygen mixture is fed into the bottom of the first-stage high-pressure tower via a feed pump for adsorption. The top of the first-stage high-pressure tower collects the mixed gas; a portion of this top gas is output as a light component, and the other portion is refluxed to flush the first-stage low-pressure tower as a light component mixture. The top of the first-stage low-pressure tower is flushed with the light component mixture, while the bottom of the first-stage low-pressure tower collects the first-stage heavy component gas, which serves as the second-stage feed gas. After the adsorption step, the feed is stopped, and the first-stage high-pressure and low-pressure towers undergo a pressure equalization step. The top mixed gas is released from the top of the first-stage high-pressure tower and enters the top of the first-stage low-pressure tower for pressure equalization. After equalization, the original first-stage high-pressure tower is evacuated, reducing its pressure to low pressure, while the original first-stage low-pressure tower is pressurized, increasing its pressure to high pressure. Then, the two towers exchange their timing sequences, and pressure swing adsorption is performed cyclically. The heavy component gas is fed from the bottom of the second-stage high-pressure tower. At this time, the bottom mixture of the second-stage low-pressure tower is output. Part of the bottom mixture is output as the heavy component product gas, and the other part is fed from the bottom of the second-stage high-pressure tower as the second-stage heavy component recycle gas for a displacement step. The second-stage light component recycle gas is output from the top of the second-stage high-pressure tower and circulated back to the bottom of the first-stage low-pressure tower. After the displacement step is completed, the feeding is stopped, and the second-stage high-pressure tower and the second-stage low-pressure tower undergo a pressure equalization step. During the pressure equalization process, the residual second-stage light component recycle gas in the second-stage high-pressure tower is released from the top of the second-stage high-pressure tower and enters the top of the second-stage low-pressure tower for pressure equalization. After the pressure equalization is completed, the original second-stage high-pressure tower is evacuated, and the pressure inside the tower drops to low pressure. The original second-stage low-pressure tower is pressurized, and the pressure inside the tower rises to high pressure. Then, the two towers exchange their timing and cycle through pressure swing adsorption. The interiors of the first-stage high-pressure tower, the first-stage low-pressure tower, the second-stage high-pressure tower, and the second-stage low-pressure tower are each independently filled with methane adsorption material.
[0008] Preferably, the volume concentration of methane in the methane-nitrogen-oxygen mixture is 4-10%.
[0009] Preferably, the volume ratio of the top mixed gas output as light component to the top mixed gas used as light component mixed gas for reflux flushing the first-stage low-pressure tower is 1~3:4~13; the volume ratio of the bottom mixed gas used as second-stage heavy component circulating gas for reflux to the second-stage high-pressure tower for the displacement step to the bottom mixed gas output as heavy component product gas is 14~17:8~10.
[0010] Preferably, the gas mixture at the top of the tower is a nitrogen-oxygen mixture, and the volume concentration of the nitrogen-oxygen mixture is 97.9-99.1%.
[0011] Preferably, the first-order heavy component gas is methane gas, and the volume concentration of the methane gas is 24-36%.
[0012] Preferably, the bottom gas mixture is methane gas, and the volume concentration of the methane gas is 35-65%.
[0013] Preferably, the initial pressure of the first-stage high-pressure tower and the second-stage high-pressure tower is independently 0.1~0.11 MPa; the initial pressure of the first-stage low-pressure tower and the second-stage low-pressure tower is independently 0.012~0.015 MPa.
[0014] Preferably, the first-stage high-pressure tower, the first-stage low-pressure tower, the second-stage high-pressure tower, and the second-stage low-pressure tower are each independently filled with the same weight of methane adsorption material; the methane adsorption material is a carbon molecular sieve separation material.
[0015] Preferably, the gas source used for pressurizing the first-stage low-pressure tower is second-stage light component circulating gas; the gas source used for pressurizing the second-stage low-pressure tower is second-stage heavy component circulating gas.
[0016] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. The two-stage double-reflux pressure swing adsorption separation method for methane-nitrogen-oxygen mixed gas described in this invention can be carried out at room temperature and relatively low adsorption pressure, resulting in low energy consumption and cost. It is suitable for separating methane-nitrogen-oxygen mixed gas with low methane concentration, and is particularly suitable for the industrial treatment of low-concentration methane coalbed methane, yielding high-purity, high-recovery heavy component product gas (methane). Compared with cryogenic distillation and membrane separation technologies, this method has advantages such as flexible equipment, small scale, low cost, and mature technology, making it more suitable for the treatment of low-concentration methane coalbed methane and the field of methane enrichment and recovery. 2. The dual-reflux pressure swing adsorption separation method of the present invention can overcome thermodynamic limitations and achieve efficient separation of methane-nitrogen-oxygen mixture with low methane concentration, thereby effectively purifying low-concentration methane coalbed methane. It solves the technical problems of low methane recovery rate and low enrichment concentration in traditional processes, enriches methane products in low-concentration methane coalbed methane, and greatly improves the utilization value of low-concentration methane coalbed methane. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0018] Figure 1 This is a flowchart of the two-stage double reflux pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture under a certain time sequence in Embodiment 1 of the present invention; Among them, B-1 is the first-stage high-pressure tower; B-2 is the first-stage low-pressure tower; B-3 is the second-stage high-pressure tower; B-4 is the second-stage low-pressure tower; and T-1 to T-4 are buffer tanks. Detailed Implementation
[0019] This invention provides a two-stage method for the separation of a methane-nitrogen-oxygen mixture using dual reflux pressure swing adsorption, comprising the following steps: A methane-nitrogen-oxygen mixture is fed into the bottom of the first-stage high-pressure tower B-1 via a feed pump for adsorption. The top mixture of the first-stage high-pressure tower B-1 is collected; a portion is output as a light component, and the other portion is refluxed to flush the first-stage low-pressure tower B-2 as a light component mixture. The top of the first-stage low-pressure tower B-2 is flushed with the light component mixture, and the bottom of the first-stage low-pressure tower B-2 is collected as a first-stage heavy component gas. Second-stage feed gas; after the adsorption step is completed, the feed is stopped, and the first-stage high-pressure tower B-1 and the first-stage low-pressure tower B-2 undergo a pressure equalization step. The mixed gas at the top of the towers is released from the top of the first-stage high-pressure tower B-1 and enters the top of the first-stage low-pressure tower B-2 for pressure equalization. After the pressure equalization is completed, the original first-stage high-pressure tower B-1 is evacuated, and the pressure inside the tower drops to low pressure. The original first-stage low-pressure tower B-2 completes the pressurization, and the pressure inside the tower rises to high pressure. Then, the two towers exchange their timing sequences and cycle through pressure swing adsorption. The heavy component gas is fed from the bottom of the second-stage high-pressure tower B-3. At the same time, the bottom mixture of the second-stage low-pressure tower B-4 is output. Part of the bottom mixture is output as the heavy component product gas, and the other part is fed from the bottom of the second-stage high-pressure tower B-3 as the second-stage heavy component recycle gas for a displacement step. The second-stage light component recycle gas is output from the top of the second-stage high-pressure tower B-3 and circulated back to the bottom of the first-stage low-pressure tower B-2. After the displacement step is completed, the feeding is stopped, and the second-stage high-pressure tower B-3 and the second-stage low-pressure tower B-4 undergo a pressure equalization step. During the pressure equalization process, the residual second-stage light component recycle gas in the second-stage high-pressure tower is released from the top of the second-stage high-pressure tower B-3 and enters the top of the second-stage low-pressure tower B-4 for pressure equalization. After the pressure equalization is completed, the original second-stage high-pressure tower B-3 is evacuated, and the pressure inside the tower drops to low pressure. The original second-stage low-pressure tower B-4 is pressurized, and the pressure inside the tower rises to high pressure. Then, the two towers exchange their timing and cycle through pressure swing adsorption. The interiors of the first-stage high-pressure tower B-1, the first-stage low-pressure tower B-2, the second-stage high-pressure tower B-3, and the second-stage low-pressure tower B-4 are all independently filled with methane adsorption material.
[0020] In this invention, the volume concentration of methane in the methane-nitrogen-oxygen mixture is 4-10%, preferably one of 4%, 5%, 6%, 7%, 8%, 9%, and 10%.
[0021] In this invention, the volume ratio of the top mixed gas output as light component to the top mixed gas used as light component mixed gas for reflux flushing the first-stage low-pressure tower B-2 is 1~3:4~13, preferably one of 1:4, 1:5, 1:6, 1:8, 1:10, 1:11, 1:13, 2:9, 2:13, 3:11, 3:12, and 3:13; the volume ratio of the bottom mixed gas used as second-stage heavy component circulating gas for reflux to the second-stage high-pressure tower B-3 for the displacement step to the bottom mixed gas output as heavy component product gas is 14~17:8~10, preferably one of 14:8, 14:9, 14:10, 15:8, 15:9, 15:10, 16:8, 16:9, 16:10, 17:8, 17:9, and 17:10.
[0022] In this invention, the gas mixture at the top of the tower is a nitrogen-oxygen mixture, and the volume concentration of the nitrogen-oxygen mixture is 97.9-99.1%, preferably 98-99%, more preferably 98.2-98.9%, and even more preferably 98.5-98.8%.
[0023] In this invention, the first-order heavy component gas is methane gas, and the volume concentration of the methane gas is 24-36%, preferably 25-35%, more preferably 26-32%, and even more preferably 28-30%.
[0024] In this invention, the bottom gas mixture is methane gas, and the volume concentration of the methane gas is 35-65%, preferably 36-62%, more preferably 40-60%, and even more preferably 50-55%.
[0025] In this invention, the initial pressure of the first-stage high-pressure tower B-1 and the second-stage high-pressure tower B-3 is preferably 0.1~0.11 MPa; the initial pressure of the first-stage low-pressure tower B-2 and the second-stage low-pressure tower B-4 is preferably 0.012~0.015 MPa, more preferably 0.013~0.014 MPa.
[0026] In this invention, the adsorption pressure of the first-stage high-pressure tower B-1, the first-stage low-pressure tower B-2, the second-stage high-pressure tower B-3, and the second-stage low-pressure tower B-4 is preferably 0.135~0.14 MPa, and more preferably 0.136~0.138 MPa.
[0027] In this invention, the interiors of the first-stage high-pressure tower B-1, the first-stage low-pressure tower B-2, the second-stage high-pressure tower B-3, and the second-stage low-pressure tower B-4 are each independently filled with the same weight of methane adsorption material; the methane adsorption material is a carbon molecular sieve separation material; the carbon molecular sieve separation material has the advantages of large specific surface area, high separation selectivity, and high methane adsorption capacity, and the separation coefficient of the carbon molecular sieve separation material for methane and nitrogen-oxygen is greater than 5, which can effectively separate the methane-nitrogen-oxygen mixture through pressure swing adsorption process.
[0028] In this invention, the gas source used for pressurizing the first-stage low-pressure tower B-2 is the second-stage light component circulating gas; the gas source used for pressurizing the second-stage low-pressure tower B-4 is the second-stage heavy component circulating gas.
[0029] In this invention, a first buffer tank T-1 is preferably installed on the pipeline through which a portion of the tower top mixed gas is output as a light component; a second buffer tank T-2 is preferably installed before the first-stage heavy component gas is fed from the bottom of the second-stage high-pressure tower B-3; a third buffer tank T-3 is preferably installed on the pipeline through which another portion of the tower bottom mixed gas is output as a heavy component product gas; and a fourth buffer tank T-4 is preferably installed before the second-stage light component circulating gas is circulated back to the bottom of the first-stage high-pressure tower B-1 for feeding.
[0030] In this invention, the second-stage light component circulating gas is stored in the fourth buffer tank T-4 before circulating back to the bottom of the first-stage low-pressure tower B-2. When the first-stage low-pressure tower B-2 needs to be pressurized, the valve of the fourth buffer tank T-4 is opened to allow the second-stage light component circulating gas to enter the first-stage low-pressure tower B-2 for pressurization.
[0031] In this invention, the first-stage high-pressure tower B-1, the first-stage low-pressure tower B-2, the second-stage high-pressure tower B-3, and the second-stage low-pressure tower B-4 all undergo six steps: feed adsorption, pressure equalization and drop, vacuuming, light component reflux rinsing, pressure equalization and rise, and final pressure rise.
[0032] In this invention, the replacement step is essentially an adsorption step performed by the second-stage high-pressure tower B-3. The gas adsorbed (replaced) is mainly the second-stage heavy component circulating gas discharged from the bottom of the second-stage low-pressure tower B-4. The methane concentration in this circulating gas is high, which can more effectively remove nitrogen / oxygen from the tower and improve the tower's absorption of methane.
[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0034] Example 1
[0035] Low-concentration methane coalbed methane (a mixture of methane, nitrogen, and oxygen, with a methane volume concentration of 5%) is fed into the bottom of a first-stage high-pressure tower (initial pressure 0.11 MPa, packed with 175 g of carbon molecular sieve separation material) via a feed pump. After feeding, the pressure in the first-stage high-pressure tower reaches 0.135 MPa, and the adsorption step is performed. A top mixture (a nitrogen-oxygen mixture with a volume concentration of 98.7%) is collected from the top of the first-stage high-pressure tower. A portion of the top mixture is output as a light component, and the other portion is used as a light component mixture to reflux and flush the first-stage low-pressure tower (initial pressure 0.012 MPa, packed with 175 g of carbon molecular sieve separation material). (g of carbon molecular sieve separation material), wherein the volume ratio of the overhead mixed gas as the light component output to the overhead mixed gas as the light component reflux flushing of the first-stage low-pressure tower is 1:4. The top of the first-stage low-pressure tower is flushed with the light component mixed gas, and the bottom of the first-stage low-pressure tower is collected as the first-stage heavy component gas (methane gas with a volume concentration of 31%), which is used as the second-stage feed gas; after the adsorption step reaches 60 s, the feed is stopped, and the first-stage high-pressure tower and the first-stage low-pressure tower undergo a pressure equalization step. The overhead mixed gas is released from the top of the first-stage high-pressure tower and enters the top of the first-stage low-pressure tower for pressure equalization. After the pressure equalization is completed, the original first-stage high-pressure tower is evacuated, and the pressure inside the tower drops to low pressure (0.012 MPa). The original first-stage low-pressure tower completes the pressure increase, and the pressure inside the tower rises to high pressure (0.11 MPa). Afterwards, the two towers are switched in sequence for cyclic pressure swing adsorption (PSA), where the gas source used for pressurizing the first-stage low-pressure tower is the second-stage light component recycle gas). The first-stage heavy component gas is fed from the bottom of the second-stage high-pressure tower (initial pressure 0.11 MPa, packed with 175 g of carbon molecular sieve separation material). At this time, the bottom mixed gas (48% methane gas by volume) of the second-stage low-pressure tower (initial pressure 0.012 MPa, packed with 175 g of carbon molecular sieve separation material) is output from the bottom. Part of the bottom mixed gas is output as the heavy component product gas, and the other part of the bottom mixed gas is fed from the bottom of the second-stage high-pressure tower as the second-stage heavy component recycle gas. After feeding, the pressure of the second-stage high-pressure tower reaches 0.14 MPa. At a pressure of MPa, a displacement step is performed, while the second-stage high-pressure tower outputs second-stage light component circulating gas from the top, which is then circulated back to the bottom of the first-stage low-pressure tower. The volume ratio of the bottom mixture gas (returned to the second-stage high-pressure tower as the second-stage heavy component circulating gas for the displacement step) to the bottom mixture gas (output as the heavy component product gas) is 7:4. After 60 seconds of displacement, feeding is stopped, and the second-stage high-pressure and second-stage low-pressure towers undergo a pressure equalization step. During this process, the residual second-stage light component circulating gas in the second-stage high-pressure tower is released from the top of the high-pressure tower and enters the top of the second-stage low-pressure tower for pressure equalization. After equalization, the original second-stage high-pressure tower is evacuated, reducing the pressure inside to low pressure (0.012 MPa), while the original second-stage low-pressure tower is pressurized, increasing the pressure inside to high pressure (0.11 MPa). Afterward, the two towers exchange timings and cycle through pressure swing adsorption (the gas source for pressurization in the second-stage low-pressure tower is the second-stage heavy component circulating gas).
[0036] The flowchart for separating the methane-nitrogen-oxygen mixture at a certain time sequence in this embodiment is as follows: Figure 1 As shown.
[0037] According to the test results, the final methane gas obtained at the bottom of the tower in this embodiment has a volume concentration of 48%, and the recovery rate is 82%.
[0038] Example 2
[0039] Low-concentration methane coalbed methane (a mixture of methane, nitrogen, and oxygen, with a methane volume concentration of 4%) is fed into the bottom of a first-stage high-pressure tower (initial pressure 0.11 MPa, packed with 175 g of carbon molecular sieve separation material) via a feed pump. After feeding, the pressure in the first-stage high-pressure tower reaches 0.135 MPa, and the adsorption step is performed. A top mixed gas (a nitrogen-oxygen mixture with a volume concentration of 99.1%) is collected from the top of the first-stage high-pressure tower. A portion of the top mixed gas is output as a light component, and the other portion is used as a light component mixture to reflux and flush the first-stage low-pressure tower (initial pressure 0.012 MPa, packed with 175 g of carbon molecular sieve separation material). (g of carbon molecular sieve separation material), wherein the volume ratio of the overhead mixed gas as the light component output to the overhead mixed gas as the light component reflux flushing of the first-stage low-pressure tower is 3:13. The top of the first-stage low-pressure tower is flushed with the light component mixed gas, and the bottom of the first-stage low-pressure tower is collected as the first-stage heavy component gas (methane gas with a volume concentration of 26.1%), which is used as the second-stage feed gas. After the adsorption step reaches 60 s, the feed is stopped, and the first-stage high-pressure tower and the first-stage low-pressure tower undergo a pressure equalization step. The overhead mixed gas is released from the top of the first-stage high-pressure tower and enters the top of the first-stage low-pressure tower for pressure equalization. After the pressure equalization is completed, the original first-stage high-pressure tower is evacuated, and the pressure inside the tower drops to a low pressure (0.012 MPa). The original first-stage low-pressure tower completes the pressure increase, and the pressure inside the tower rises to a high pressure (0.11 MPa). Afterwards, the two towers are switched in sequence for cyclic pressure swing adsorption (PSA), where the gas source used for pressurizing the first-stage low-pressure tower is the second-stage light component recycle gas). The first-stage heavy component gas is fed from the bottom of the second-stage high-pressure tower (initial pressure 0.11 MPa, packed with 175 g of carbon molecular sieve separation material). At this time, the bottom mixed gas (38.5% methane gas by volume concentration) of the second-stage low-pressure tower (initial pressure 0.012 MPa, packed with 175 g of carbon molecular sieve separation material) is output from the bottom of the tower. Part of the bottom mixed gas is output as the heavy component product gas, and the other part of the bottom mixed gas is fed from the bottom of the second-stage high-pressure tower as the second-stage heavy component recycle gas. After feeding, the pressure of the second-stage high-pressure tower reaches 0.14 MPa. The pressure is increased to MPa, and a displacement step is performed. Simultaneously, the second-stage high-pressure tower outputs second-stage light component circulating gas from the top, which is then circulated back to the bottom of the first-stage low-pressure tower. The volume ratio of the bottom mixture gas (returned to the second-stage high-pressure tower as the second-stage heavy component circulating gas) to the bottom mixture gas (output as the heavy component product gas) is 17:10. After 60 seconds of displacement, feeding is stopped, and the second-stage high-pressure tower and the second-stage low-pressure tower undergo a pressure equalization step. During this process, the residual second-stage light component circulating gas in the second-stage high-pressure tower is released from the top of the second-stage high-pressure tower and enters the top of the second-stage low-pressure tower for pressure equalization. After pressure equalization, the original second-stage high-pressure tower is evacuated, and the pressure inside the tower drops to a low pressure (0.012 MPa). The original second-stage low-pressure tower completes its pressure increase, and the pressure inside the tower rises to a high pressure (0.012 MPa).(11 MPa); then, the two towers exchange timing sequences and cycle through pressure swing adsorption (wherein, the gas source used for pressurization in the second-stage low-pressure tower is the second-stage heavy component recirculation gas).
[0040] According to the test results, the final methane gas obtained at the bottom of the tower in this embodiment has a volume concentration of 45%, and the recovery rate is 80.4%.
[0041] Example 3
[0042] Low-concentration methane coalbed methane (a mixture of methane, nitrogen, and oxygen, with a methane volume concentration of 10%) is fed into the bottom of a first-stage high-pressure tower (initial pressure 0.11 MPa, packed with 175 g of carbon molecular sieve separation material) via a feed pump. After feeding, the pressure in the first-stage high-pressure tower reaches 0.135 MPa, and the adsorption step is performed. A top mixed gas (a nitrogen-oxygen mixture with a volume concentration of 97.9%) is collected from the top of the first-stage high-pressure tower. A portion of the top mixed gas is output as a light component, and the other portion is used as a light component mixture to reflux and flush the first-stage low-pressure tower (initial pressure 0.012 MPa, packed with 175 g of carbon molecular sieve separation material). (g of carbon molecular sieve separation material), wherein the volume ratio of the overhead mixed gas as the light component output to the overhead mixed gas as the light component reflux flushing of the first-stage low-pressure tower is 3:11. The top of the first-stage low-pressure tower is flushed with the light component mixed gas, and the bottom of the first-stage low-pressure tower is collected as the first-stage heavy component gas (methane gas with a volume concentration of 35.7%), which is used as the second-stage feed gas. After the adsorption step reaches 60 s, the feed is stopped, and the first-stage high-pressure tower and the first-stage low-pressure tower undergo a pressure equalization step. The overhead mixed gas is released from the top of the first-stage high-pressure tower and enters the top of the first-stage low-pressure tower for pressure equalization. After the pressure equalization is completed, the original first-stage high-pressure tower is evacuated, and the pressure inside the tower drops to a low pressure (0.012 MPa). The original first-stage low-pressure tower completes the pressure increase, and the pressure inside the tower rises to a high pressure (0.11 MPa). Afterwards, the two towers are switched in sequence for cyclic pressure swing adsorption (PSA), where the gas source used for pressurizing the first-stage low-pressure tower is the second-stage light component recycle gas). The first-stage heavy component gas is fed from the bottom of the second-stage high-pressure tower (initial pressure 0.11 MPa, packed with 175 g of carbon molecular sieve separation material). At this time, the bottom mixed gas (61.9% methane gas by volume concentration) of the second-stage low-pressure tower (initial pressure 0.012 MPa, packed with 175 g of carbon molecular sieve separation material) is output from the bottom. Part of the bottom mixed gas is output as the heavy component product gas, and the other part of the bottom mixed gas is fed from the bottom of the second-stage high-pressure tower as the second-stage heavy component recycle gas. After feeding, the pressure of the second-stage high-pressure tower reaches 0.14 MPa. The pressure is increased to MPa, and a displacement step is performed. Simultaneously, the second-stage high-pressure tower outputs second-stage light component circulating gas from the top, which is then circulated back to the bottom of the first-stage low-pressure tower. The volume ratio of the bottom mixture gas (returned to the second-stage high-pressure tower as the second-stage heavy component circulating gas for the displacement step) to the bottom mixture gas (output as the heavy component product gas) is 17:10. After the displacement step, feeding is stopped, and the second-stage high-pressure tower and the second-stage low-pressure tower undergo a pressure equalization step. During this process, the residual second-stage light component circulating gas in the second-stage high-pressure tower is released from the top of the second-stage high-pressure tower and enters the top of the second-stage low-pressure tower for pressure equalization. After pressure equalization, the original second-stage high-pressure tower is evacuated, and the pressure inside the tower drops to a low pressure (0.012 MPa). The original second-stage low-pressure tower completes its pressure increase, and the pressure inside the tower rises to a high pressure (0.012 MPa).(11 MPa); then, the two towers exchange timing sequences and cycle through pressure swing adsorption (wherein, the gas source used for pressurization in the second-stage low-pressure tower is the second-stage heavy component recirculation gas).
[0043] According to the test results, the final methane gas obtained at the bottom of the tower in this embodiment has a volume concentration of 50%, and the recovery rate is 84.6%.
[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture, characterized in that, Includes the following steps: A methane-nitrogen-oxygen mixture is fed into the bottom of the first-stage high-pressure tower via a feed pump for adsorption. The top of the first-stage high-pressure tower collects the mixed gas; a portion of this top gas is output as a light component, and the other portion is refluxed to flush the first-stage low-pressure tower as a light component mixture. The top of the first-stage low-pressure tower is flushed with the light component mixture, while the bottom of the first-stage low-pressure tower collects the first-stage heavy component gas, which serves as the second-stage feed gas. After the adsorption step, the feed is stopped, and the first-stage high-pressure and low-pressure towers undergo a pressure equalization step. The top mixed gas is released from the top of the first-stage high-pressure tower and enters the top of the first-stage low-pressure tower for pressure equalization. After equalization, the original first-stage high-pressure tower is evacuated, reducing its pressure to low pressure, while the original first-stage low-pressure tower is pressurized, increasing its pressure to high pressure. Then, the two towers exchange their timing sequences, and pressure swing adsorption is performed cyclically. The heavy component gas is fed from the bottom of the second-stage high-pressure tower. At this time, the bottom mixture of the second-stage low-pressure tower is output. Part of the bottom mixture is output as the heavy component product gas, and the other part is fed from the bottom of the second-stage high-pressure tower as the second-stage heavy component recycle gas for a displacement step. The second-stage light component recycle gas is output from the top of the second-stage high-pressure tower and circulated back to the bottom of the first-stage low-pressure tower. After the displacement step is completed, the feeding is stopped, and the second-stage high-pressure tower and the second-stage low-pressure tower undergo a pressure equalization step. During the pressure equalization process, the residual second-stage light component recycle gas in the second-stage high-pressure tower is released from the top of the second-stage high-pressure tower and enters the top of the second-stage low-pressure tower for pressure equalization. After the pressure equalization is completed, the original second-stage high-pressure tower is evacuated, and the pressure inside the tower drops to low pressure. The original second-stage low-pressure tower is pressurized, and the pressure inside the tower rises to high pressure. Then, the two towers exchange their timing and cycle through pressure swing adsorption. The interiors of the first-stage high-pressure tower, the first-stage low-pressure tower, the second-stage high-pressure tower, and the second-stage low-pressure tower are each independently filled with methane adsorption material.
2. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 1, characterized in that, The volume concentration of methane in the methane-nitrogen-oxygen mixture is 4-10%.
3. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 2, characterized in that, The volume ratio of the overhead mixed gas output as a light component to the overhead mixed gas used for reflux flushing the first-stage low-pressure column as a light component mixed gas is 1~3:4~13. The volume ratio of the bottom mixture gas, which is used as the circulating gas for the second-stage heavy component and refluxed to the second-stage high-pressure tower for the displacement step, to the bottom mixture gas, which is used as the product gas for the heavy component, is 14~17:8~10.
4. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to any one of claims 1 to 3, characterized in that, The gas mixture at the top of the tower is a nitrogen-oxygen mixture with a volume concentration of 97.9-99.1%.
5. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 4, characterized in that, The first-order heavy component gas is methane gas, and the volume concentration of the methane gas is 24-36%.
6. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 5, characterized in that, The bottom gas mixture is methane gas, and the volume concentration of the methane gas is 35-65%.
7. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 6, characterized in that, The initial pressures of the first-stage high-pressure tower and the second-stage high-pressure tower are independent, ranging from 0.1 to 0.11 MPa. The initial pressures of the first-stage low-pressure tower and the second-stage low-pressure tower are independent and range from 0.012 to 0.015 MPa.
8. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 7, characterized in that, The first-stage high-pressure tower, the first-stage low-pressure tower, the second-stage high-pressure tower, and the second-stage low-pressure tower are all independently filled with the same weight of methane adsorption material. The methane adsorption material is a carbon molecular sieve separation material.
9. The two-stage pressure swing adsorption separation method for a methane-nitrogen-oxygen mixture according to claim 8, characterized in that, The gas source used for pressurizing the first-stage low-pressure tower is second-stage light component circulating gas; the gas source used for pressurizing the second-stage low-pressure tower is second-stage heavy component circulating gas.